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Entities in MGCP

There are four basic entities in MGCP:

Endpoint

A media gateway is a collection of endpoints. An endpoint can be an analog line, trunk, or any other access point. An endpoint contains the following elements:



local-endpoint-name@domain-name

The following examples are some valid endpoint IDs:



group1/Trk8@mynetwork.net
group2/Trk1/*@[192.168.10.8] (wild-carding)
$@voiptel.net (any endpoint within the media gateway)
*@voiptel.net (all endpoints within the media gateway)

Connection

Connections are created on each endpoint by an MG during call setup. A typical VoIP call involves two connections. A complex call, for example a three-party call or conference call, might require more connections. The media gateway controller (MGC) can instruct media gateways to create, modify, delete and audit a connection.

A connection is identified by its connection ID which is created by the MG when it is requested to create a connection. Connection ID is presented as a hexadecimal string, and its maximum length is 32 characters

Call

A call is identified by its call ID, which is created by the MGC when establishing a new call. Call ID is a hexadecimal string with a maximum length of 32 characters. Call ID is unique within the MGC. Two or more connections can have the same call ID if they belong to the same call.

Call Agent

One or more call agents (also called media gateway controllers) are supported in MGCP to enhance reliability in the VoIP network. The following two examples are of call agent names:



CallAgent@voipCA.mynetwork.com
voipCA.mynetwork.com

Several network addresses can be associated under one domain name in the Domain Name System (DNS). By keeping track of the time to live (TTL) of DNS query/response data and implementing retransmission using other alternative network addresses, switchover and failover is achieved in MGCP.

The concept of a notified entity is essential in MGCP. The notified entity for an endpoint is the call agent currently controlling that endpoint. An endpoint should send any MGCP command to its notified entity. However, different call agents might send MGCP commands to this endpoint.

The notified entity is set to a provisioned value upon startup, but can be changed by a call agent through the use of the NotifiedEntity parameter contained in an MGCP message. If the notified entity for an endpoint is empty or has not been set explicitly, its value defaults to the source address of the last successful non-audit MGCP command received for that endpoint.

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